Cellulose ester film and its manufacturing method, optical film, polarizing plate and liquid crystal display

Abstract

Disclosed is a cellulose ester film containing cellulose ester and microparticles having an average primary particle diameter of from 0.1 to 1.0 μm, wherein a relative standard deviation of a primary particle diameter of the microparticles is from 1 to 20%, and wherein the cellulose ester film has a surface with a peak density of from 1,000 to 8,000 (1 / mm2).

Description

[0001]This application is based on Japanese Patent Application Nos. 2004-168647 filed on Jun. 7, 2004, and 2005-072201 fined on Mar. 15, 2005 in Japanese Patent Office, the entire content of which is hereby incorporated by reference.FIELD OF THE INVENTION[0002]The present invention relates to a cellulose ester film for optical use (hereinafter also referred to as a film) and its manufacturing method, and particularly to a cellulose ester film used in a polarizing plate protective film, a retardation film or a viewing angle increasing film for a liquid crystal display, in functional films for a plasma display such as an antireflection film, or in functional films for an organic EL display and its manufacturing method, and to an optical film, a polarizing plate and a liquid crystal display employing the cellulose ester film.BACKGROUND OF THE INVENTION[0003]Recently, study and development has been made regarding decrease in thickness and weight of a note board type personal computer, e...

AI Technical Summary

Benefits of technology

[0040]The microparticles in the invention is preferably microcapsules obtained by hydrolytic condensation of a reactive silicon compound. This method can adjust easily the relative standard deviation of the average primary particle diameter, exhibiting the effects of the invention. For example, there is a method disclosed in Japanese Patent Publication No. 5-4325 in which an alkoxysilane compound in the organic solution is hydrolytically condensed in the presence of excessive water, or a method disclosed in Japanese Patent No. 348461 in which an alkoxysilane compound in the gaseous phase is hydrolytically condensed in the presence of water droplets. There is, further, a method disclosed in Japanese Patent Publication No. 6-57317 in which microcapsules are dispersed in glycol, or a method disclosed in Japanese Patent No. 318752.

[0041]The cellulose ester film has a surface peak density of from 1,000 to 8,000 (1 / mm2), preferably from 2,000 to 6,000 (1 / mm2), and more preferably from 3,000 to 5,000 (1 / mm2). The above surface peak density range is preferred, since a greater surface peak density exhibits better sliding property, while a less surface peak density better transparency. The above surface peak density range can be obtained by adjusting the above average primary particle diameter of the microparticles and the above relative standard deviation of the particle diameter of the microcapsules. The microparticle content of the cellulose ester film of the invention is preferably from 0.02 to 1.0 g / m2, more preferably from 0.03 to 0.3 g / m2, and most preferably from 0.08 to 0.2 g / m2.

[0042]In the invention, the surface peak density is measured as follows: The number of peaks with a height of not less than 3 nm (preferably from 3 to 500 nm) on the film surface is measured at 23° C. and at a relative humidity RH of 50%+5% RH at an objective lens magnification of 50 and at an image zoom magnification of 1.0, employing a three dimensional surface structure analysis microscope zygo new View 5000 available from Canon Sales Co., Inc., and divided by an area measured to obtain the number per 1 mm2 of the peaks. In the invention, the surface peak density is represented in terms of the peak number per mm2 of the film.

[0043]In order to incorporate the microparticles in the invention into the cellulose ester film, an addition solution containing the microparticles is added to a dope as described later. A main dope to which the microparticles in powder are directly added results in insufficient dispersion, and a filter clogs with microparticle aggregates, resulting in rapid increase of filtration pressure. Therefore, it is preferred that a main dope, after added with the addition solution containing the microparticles, is filtered with for example, a filter capturing microparticles with a particle diameter of from 0.5 to 5 μm and giving a filtration time of from 10 to 25 sec / 100 ml. Incorporation of the addition solution containing the microparticles to the main dope may be any time before filtration as described above. The addition solution may be incorporated in the main dope placed in a dissolution vessel, or the main dope and the addition solution may be mixed in a mixing vessel provided separately. Before filtration, they may be mixed through a static mixer in a pipe leading to a filter. In most cases, the main dope contains return scraps in an amount of from 1.0 to 50% by weight. Since the return scraps contain microparticles, the content of the microparticles in the addition solution need to be adjusted depending upon the amount of the return scraps contained in the main dope. A method, in which the addition solution is added directly to the main dope and batch control is possible, or a method, in which the main dope and the addition solution are mixed in a mixing vessel, is preferred in view of ease of control. The former method is more preferred since time for mixing the main dope and the addition solution is sufficient and excellent productivity is obtained. The addition solution contains the microparticles in an amount of preferably from 0.5 to 10% by weight, more preferably from 1 to 5% by weight, and still more preferably from 1 to 3% by weight.

[0044]An addition solution having a low content of the microparticles is low in viscosity, which is easy to handle, while an addition solution having a high content of the microparticles can be added in a small amount to the main dope, which is easy to add. Therefore, the above microparticle content range is preferred. The return scraps herein referred to are cellulose ester pieces, for example, pieces produced by cutting the both edges of cellulose ester film web during manufacture, or cellulose ester film falling outside the specifications on account of scratches.

[0045]The main dope in the invention refers to a dope for manufacturing the cellulose ester film of the invention, and is distinguished from the addition solution. Resin, which the main dope contains in a high concentration, may be added in a small amount to the addition solution. In the invention, a dope containing most of film forming resin is referred to as the main dope, which is distinguished from the addition solution.

Problems solved by technology

However, such a film roll has problem in storage stability.

There is, for example, problem that the films are adhered to each other to deform or the films form a convex shape as if there is foreign matter between the films.

However, this method has problem in that when the amount of microparticles added to cellulose ester film is increased, it increases haze of the cellulose ester film, resulting in lowering of transparency.

It is difficult to obtain a cellulose ester film with improved sliding property and high transparency by increasing an amount of microparticles to be added to a cellulose ester film.

Therefore, there is problem in that the same Ra value may provide different effects in sliding property, haze or storage stability.

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